Sand in lakes and bogs in Allegan County, Michigan, as a proxy for eolian sand transport

Accurately reconstructing the rate of movement and extent of eolian dunes over thousands of years is a challenging endeavor. In this paper, we refine the methodology for utilizing lakes and bogs downwind of dune fields as precise recorders of past eolian activity. Sediment cores from two Allegan County lakes and one bog associated with dunes were studied to evaluate the importance of the various sand transport pathways into lakes and bogs. Goshorn Lake's western edge directly abuts a large parabolic dune. Sand concentrations decrease in cores away from the dunes, possibly reflecting avalanching into the lake followed by sediment gravity flows along the lake bottom. Sand input from stream flow was minor. The Allegan Bog core records a fenemergent bog transition coincident with a decrease in the sand influx. Poorly understood shoreline processes may have contributed sand to the basin's center before the bog's emergence. Sand in Gilligan Lake cores is texturally similar to adjacent dune sand and the eolian activity history derived from this sand is nearly identical to the history derived from the dune's paleosols and optically stimulated luminescence ages. A proposed lake and bog sampling strategy includes choosing sites in the lee of large dunes edged with emergent vegetation and away from steep slopes or stream inlets. The lake's bathymetry should also be considered. Distinguishing between grain fall sedimentary structures and mass movement or sediment gravity flows is important. This strategy provides relatively high resolution, continuous eolian activity histories that can be correlated with paleoenvironmental proxies from the same cores.